bibtex-search-forward-string is a compiled Lisp function in `bibtex.el'.

(bibtex-search-forward-string &optional EMPTY-KEY)

Search forward to find a BibTeX string entry.
If a syntactically correct entry is found, a pair containing the boundaries of
the reference key and text parts of the string is returned.
If EMPTY-KEY is non-nil, key may be empty. Do not move point.